| This Pentax zoom eyepiece is physically sized for use with the compact 65mm Pentax spotting scopes. It can also be used with the 80mm and 100mm Pentax scopes if the size and weight of the larger XW eyepieces normally used with them becomes an issue with those models. It has a variable focal length range of 19.5mm to 6.5mm. This provides a zoom range of 20x to 60x magnification with the 65mm Pentax scopes, to cover a wide range of birding and nature study situations. Its apparent field of view ranges from 42° at 20x to 60° at 60x. This provides an actual 2.1° field (110’ @ 1000 yards) at 20x and a 1° field (52.5’ @1000 yards) at 60x. (It provides a magnification range of 26x to 78x with the straight-through 80mm Pentax scope, 27x to 81x with the straight-through 80mm Pentax, and 32.5x to 97.5x with the 100mm Pentax.) The figures given to the right are with the zoom set at 20x magnification. The usable eye relief ranges from 14mm at 20x to 10mm at 60x. These somewhat-short figures will vignette the field of view for those who must wear eyeglasses while observing due to astigmatism, particularly at the higher powers. Those who do not wear glasses will find the eye relief more than acceptable for unvignetted viewing, particularly when the rubber-rimmed twist-up eyecup is extended to block out ambient light and position the eye at the correct eyepoint. The eyepiece barrel has a series of four grooves machined into the scope side of the barrel. When the eyepiece is first inserted into the scope, before tightening the eyepiece locking collar, the eyepiece should be twisted slightly until one of these grooves engages the pin in the bottom of the eyepiece receptacle. This will keep the eyepiece from twisting in place when the knurled power change collar on the eyepiece is turned to adjust the magnification. All lens elements (a sophisticated 6 lens/4 group design) are fully multicoated with Pentax SMC (Super Multi-Coated) high transmission antireflection optical coatings for maximum light transmission and contrast. High refraction/low dispersion glass elements are used for excellent color fidelity. The eyepiece is specially sealed to be weatherproof under the worst observing conditions a birder might encounter, short of total submersion. Protective caps are provided for both ends of the eyepiece.
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